The logic of gicv3_redist_update() is as follows:
* it must be called in any code path that changes the state of
(only) redistributor interrupts
* if it finds a redistributor interrupt that is (now) higher
priority than the previous highest-priority pending interrupt,
then this must be the new highest-priority pending interrupt
* if it does *not* find a better redistributor interrupt, then:
- if the previous state was "no interrupts pending" then
the new state is still "no interrupts pending"
- if the previous best interrupt was not a redistributor
interrupt then that remains the best interrupt
- if the previous best interrupt *was* a redistributor interrupt,
then the new best interrupt must be some non-redistributor
interrupt, but we don't know which so must do a full scan
In commit 17fb5e36aa we effectively added the LPI interrupts
as a kind of "redistributor interrupt" for this purpose, by adding
cs->hpplpi to the set of things that gicv3_redist_update() considers
before it gives up and decides to do a full scan of distributor
interrupts. However we didn't quite get this right:
* the condition check for "was the previous best interrupt a
redistributor interrupt" must be updated to include LPIs
in what it considers to be redistributor interrupts
* every code path which updates the LPI state which
gicv3_redist_update() checks must also call gicv3_redist_update():
this is cs->hpplpi and the GICR_CTLR ENABLE_LPIS bit
This commit fixes this by:
* correcting the test on cs->hppi.irq in gicv3_redist_update()
* making gicv3_redist_update_lpi() always call gicv3_redist_update()
* introducing a new gicv3_redist_update_lpi_only() for the one
callsite (the post-load hook) which must not call
gicv3_redist_update()
* making gicv3_redist_lpi_pending() always call gicv3_redist_update(),
either directly or via gicv3_redist_update_lpi()
* removing a couple of now-unnecessary calls to gicv3_redist_update()
from some callers of those two functions
* calling gicv3_redist_update() when the GICR_CTLR ENABLE_LPIS
bit is cleared
(This means that the not-file-local gicv3_redist_* LPI related
functions now all take care of the updates of internally cached
GICv3 information, in the same way the older functions
gicv3_redist_set_irq() and gicv3_redist_send_sgi() do.)
The visible effect of this bug was that when the guest acknowledged
an LPI by reading ICC_IAR1_EL1, we marked it as not pending in the
LPI data structure but still left it in cs->hppi so we would offer it
to the guest again. In particular for setups using an emulated GICv3
and ITS and using devices which use LPIs (ie PCI devices) a Linux
guest would complain "irq 54: nobody cared" and then hang. (The hang
was intermittent, presumably depending on the timing between
different interrupts arriving and being completed.)
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Tested-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Message-id: 20211124202005.989935-1-peter.maydell@linaro.org